Organic light emitting diode display having high aperture ratio and method for manufacturing the same

ABSTRACT

The present disclosure relates to an organic light emitting diode display having high aperture ratio and a method for manufacturing the same. The present disclosure suggests an organic light emitting diode display comprising: a plurality of pixel areas disposed in a matrix manner on a substrate; a thin film transistor disposed in the pixel area; an organic light emitting diode connected to the thin film transistor and disposed in the pixel area; and a three-stack storage capacitor having four electrodes connected to the thin film transistor and the organic light emitting diode.

This application claims the benefit of Korean Patent Application No.10-2013-0101623 filed on Aug. 27, 2013, which is incorporated herein byreference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to an organic light emitting diodedisplay having high aperture ratio and a method for manufacturing thesame. Especially, the present disclosure relates to a bottom emissiontype organic light emitting diode display and a method for manufacturingthe same, in which the four electrodes are overlapped each other forforming the storage capacitor ensuring more storage capacitor withminimized plane area.

2. Discussion of the Related Art

Nowadays, various flat panel display devices are developed forovercoming many drawbacks of the cathode ray tube such as heavy weightand bulk volume. The flat panel display devices include the liquidcrystal display device (or LCD), the field emission display (or FED),the plasma display panel (or PDP) and the electroluminescence device (orEL).

The electroluminescence display device is categorized in the inorganiclight emitting diode display device and the organic light emitting diodedisplay device according to the luminescence material. As aself-emitting display device, the electroluminescence display device hasthe merits those the response speed is very fast, the brightness is veryhigh and the view angle is large.

FIG. 1 is a diagram illustrating the structure of the organic lightemitting diode. As shown in FIG. 1, the organic light emitting diodecomprises the organic light emitting material layer, and the cathode andthe anode which are facing each other with the organic light emittingmaterial layer therebetween. The organic light emitting material layercomprises the hole injection layer HIL, the hole transport layer HTL,the emission layer EML, the electron transport layer ETL and theelectron injection layer EIL. The organic light emitting diode radiatesthe lights due to the energy from the excition formed at the excitationstate in which the hole and the electron are recombined at the emissionlayer EML.

The organic light emitting diode radiates the lights due to the energyfrom the excition formed at the excitation state in which the hole fromthe anode and the electron from the cathode are recombined at theemission layer EML. The organic light emitting diode display canrepresent the video data by controlling the amount (or ‘brightness’) ofthe light generated and radiated from the emission layer ELM of theorganic light emitting diode as shown in FIG. 1.

The organic light emitting diode display (or OLED) using the organiclight emitting diode can be categorized in the passive matrix typeorganic light emitting diode display (or PMOLED) and the active matrixtype organic light emitting diode display (or AMOLED).

The active matrix type organic light emitting diode display (or AMOLED)shows the video data by controlling the current applying to the organiclight emitting diode using the thin film transistor (or TFT).

FIG. 2 is the exemplary circuit diagram illustrating the structure ofone pixel in the active matrix organic light emitting diode display (orAMOLED). FIG. 3 is a plane view illustrating the structure of one pixelin the AMOLED. FIG. 4 is a cross sectional view along the cutting lineI-I′ for illustrating the structure of the AMOLED.

Referring to FIGS. 2 and 3, the active matrix organic light emittingdiode display comprises a switching thin film transistor ST, a drivingthin film transistor DT connected to the switching thin film transistorST, and an organic light emitting diode OLED connected to the drivingthin film transistor DT.

The switching thin film transistor ST is formed where the scan line SLand the data line DL is crossing. The switching thin film transistor STacts for selecting the pixel which is connected to the switching thinfilm transistor ST. The switching thin film transistor ST includes agate electrode SG branching from the gate line GL, a semiconductorchannel layer SA overlapping with the gate electrode SG, a sourceelectrode SS and a drain electrode SD. The driving thin film transistorDT acts for driving an anode electrode ANO of the organic light emittingdiode OD disposed at the pixel selected by the switching thin filmtransistor ST. The driving thin film transistor DT includes a gateelectrode DG connected to the drain electrode SD of the switching thinfilm transistor ST, a semiconductor channel layer DA, a source electrodeDS connected to the driving current line VDD, and a drain electrode DD.The drain electrode DD of the driving thin film transistor DT isconnected to the anode electrode ANO of the organic light emitting diodeOLED.

Referring to FIG. 4 more detail, on the substrate SUB of the activematrix organic light emitting diode display, the gate electrodes SG andDG of the switching thin film transistor ST and the driving thin filmtransistor DT, respectively are formed. On the gate electrodes SG andDG, the gate insulator GI is deposited. On the gate insulator GIoverlapping with the gate electrodes SG and DG, the semiconductor layersSA and DA are formed, respectively. On the semiconductor layer SA andDA, the source electrode SS and DS and the drain electrode SD and DDfacing and separating from each other are formed. The drain electrode SDof the switching thin film transistor ST is connected to the gateelectrode DG of the driving thin film transistor DT via the contact holepenetrating the gate insulator GI. The passivation layer PAS isdeposited on the substrate SUB having the switching thin film transistorST and the driving thin film transistor DT.

Especially, in the case that the semiconductor layers SA and DA includethe oxide semiconductor material, thanks to the characteristics of highelectron mobility, it has merit for applied to a large area thin filmtransistor substrate having large charging capacitor. However, in orderto ensure the stability of the oxide semiconductor material, it ispreferable to include an etch stopper SE and DE covering the uppersurface of channel area to protect them from etchants. In detail, theetch stoppers SE and DE would be formed to protect the semiconductorlayers SA and DA from being back-etched by the etchant for patterningthe source electrodes SS and DS and the drain electrodes SD and DD.

A color filer is formed at the area where the anode electrode ANO willbe formed later. It is preferable for the color filter CF to have alarge area as possible. For example, it is preferable to overlap withsome portions of the data line DL, the driving current line VDD and/orthe scan line SL. The upper surface of the substrate having these thinfilm transistors ST and DT and color filters CF is not in even and/orsmooth conditions, but in uneven and/or rugged conditions having manysteps. In order that the organic light emitting diode display has goodluminescent quality over the whole display area, the organic lightemitting layer OLE should be formed on an even or smooth surface. So, tomake the upper surface in planar and even conditions, the over coatlayer OC is deposited on the whole surface of the substrate OC.

Then, on the over coat layer OC, the anode electrode ANO of the organiclight emitting diode OLED is formed. Here, the anode electrode ANO isconnected to the drain electrode DD of the driving thin film transistorDT through the contact hole penetrating the over coat layer OC and thepassivation layer PAS.

On the substrate SUB having the anode electrode ANO, a bank BANK isformed over the area having the switching thin film transistor ST, thedriving thin film transistor DT and the various lines DL, SL and VDD,for defining the light emitting area. The exposed portion of the anodeelectrode ANO by the bank BANK would be the light emitting area. On theanode electrode ANO exposed from the bank BANK, the organic lightemitting layer OLE is formed. On the organic light emitting layer OLE,the cathode electrode ACT is formed.

For the case that the organic light emitting layer OLE has a materialemitting the white lights, each pixel can represent various colors bythe color filter CF disposed under the anode electrode ANO. The organiclight emitting diode display as shown in FIG. 4 is the bottom emissiontype display in which the visible light is radiated to the bottomdirection of the display substrate.

In the bottom emission type organic light emitting diode display, thestorage capacitor STG is formed where the gate electrode DG of thedriving thin film transistor DT and the anode electrode ANO areoverlapped. For the organic light emitting diode display, it canrepresent the video data by driving the organic light emitting diode. Ingeneral, the required energy for driving the organic light emittingdiode is higher than any other electric element used for representingvideo data.

In order to exactly and quickly represent the moving video data of whichelectric data is very quickly varied, the large amount of the storagecapacitor is required for the organic light emitting diode display. Forensuring enough storage capacitor, the surface area of the storagecapacitor should be large. For the case of the top emission type organiclight emitting diode display, as the storage capacitor can be formed byoverlapping with the emission area, it can ensure enough large area ofthe storage capacitor without reduction of the aperture ratio. On thecontrary, for the case of the bottom emission type organic lightemitting diode display, as the area of the storage capacitor is gettinglarger, the area for representing light i.e., the aperture ratio wouldbe reduced. That is, in the bottom emission type organic light emittingdiode display, the area of the storage capacitor directly affects to theaperture ratio reduction.

SUMMARY OF THE INVENTION

In order to overcome the above mentioned drawbacks, the purpose of thepresent disclosure is to suggest a bottom emission type organic lightemitting diode display in which the area of the storage capacitor isminimized for preventing the aperture ratio reduction, and a method formanufacturing the same. Another purpose of the present disclosure is tosuggest a bottom emission type organic light emitting diode display inwhich four electrodes are overlapped each other for forming the storagecapacitor so that the surface area of the storage capacitor can beminimized but the enough amount of the storage capacitor can be ensured,and a method for manufacturing the same.

In order to accomplish the above purpose, the present disclosuresuggests an organic light emitting diode display comprising: a pluralityof pixel areas disposed in a matrix manner on a substrate; a thin filmtransistor disposed in the pixel area; an organic light emitting diodeconnected to the thin film transistor and disposed in the pixel area;and a three-stack storage capacitor having four electrodes connected tothe thin film transistor and the organic light emitting diode.

In one embodiment, the thin film transistor includes: a light shieldlayer blocking external lights induced to a channel layer and being alower gate electrode; a buffer layer covering the light shield layer; asemiconductor layer having a channel layer overlapping with the lightshield layer on the buffer layer; a upper gate electrode overlappingwith the channel layer having a gate insulating layer there-between; anintermediate insulating layer covering the semiconductor layer and theupper gate electrode; and a source electrode and a drain electrodecontact some portions of the semiconductor layer disposed both sides ofthe channel layer on the intermediate insulating layer.

In one embodiment, the three-stack storage capacitor includes: a firststorage capacitor formed at some portions of the buffer layer disposedbetween an additional storage capacitor electrode and an intermediateelectrode overlapped each other; a second storage capacitor formed atsome portions of the gate insulating layer disposed between theintermediate electrode and a first storage capacitor electrodeoverlapped each other; and a third storage capacitor formed at someportions of the intermediate insulating layer disposed between the firststorage capacitor electrode and a second storage capacitor electrodeoverlapped each other.

In one embodiment, the additional storage capacitor electrode is formedat the same layer and with the same material of the light shield layer,the first storage capacitor electrode is formed at the same layer andwith the same material of the upper gate electrode, and the secondstorage capacitor electrode is extended from the drain electrode andconnected to the intermediate electrode via a contact hole through theintermediate insulating layer and the gate insulating layer.

In one embodiment, the organic light emitting diode includes: an anodeelectrode formed on a passivation layer and an over coat layer coveringthe thin film transistor, and connected to the drain electrode exposedfrom the passivation layer and the over coat layer; an organic lightemitting layer deposited on the anode electrode; and a cathode electrodedeposited on the organic light emitting layer.

In one embodiment, the organic light emitting diode further comprises acolor filter inserted between the passivation layer and the over coatlayer and configured to define a light emitting area.

In one embodiment, the anode electrode includes a transparent conductivematerial, the cathode electrode includes a reflective metal material,and lights radiated from the organic light emitting layer radiates tothe color filter.

Furthermore, the present disclosure suggests a method for manufacturingan organic light emitting diode display comprising: forming a lightshield layer and an additional storage capacitor electrode; forming abuffer layer covering the light shield layer and the additional storagecapacitor electrode; forming an intermediate electrode overlapping withthe additional storage capacitor electrode on the buffer layer; forminga semiconductor layer including a channel layer overlapping with thelight shield layer on the buffer layer; forming a upper gate electrodeoverlapping with the channel layer and a first storage capacitorelectrode overlapping with the intermediate electrode on a gateinsulating layer; forming a intermediate insulating layer covering theupper gate electrode and the first storage capacitor electrode andexposing both sides of the semiconductor layer and one end of theintermediate electrode; and forming a source electrode contacting to oneside of the semiconductor layer, and a second storage capacitorelectrode contacting to other side of the semiconductor layer and theintermediate electrode and overlapping with the first storage capacitorelectrode.

In one embodiment, a first storage capacitor is formed at some portionsof the buffer layer disposed between an additional storage capacitorelectrode and an intermediate electrode overlapped each other; a secondstorage capacitor is formed at some portions of the gate insulatinglayer disposed between the intermediate electrode and a first storagecapacitor electrode overlapped each other; and a third storage capacitoris formed at some portions of the intermediate insulating layer disposedbetween the first storage capacitor electrode and a second storagecapacitor electrode overlapped each other.

In one embodiment, the method for manufacturing the organic lightemitting diode display further comprises: depositing a passivation layercovering the source electrode, the drain electrode and the secondcapacitor electrode; forming a color filter defining a light emittingarea on the passivation layer; forming an over coat layer covering thecolor filter and exposing some portions of the drain electrode; formingan anode electrode connecting to the drain electrode and covering thecolor filter on the over coat layer; depositing an organic lightemitting layer on the anode electrode; and depositing a cathodeelectrode on the organic light emitting layer.

The organic light emitting diode display according to the presentdisclosure has the storage capacitor including four electrodesoverlapped each other, so that the area ratio of the storage capacitorto the pixel area can be minimized. Therefore, the area of thenon-display area including the storage capacitor in the pixel area canbe minimized, so that the display area can be maximized. As the result,it is possible to get a bottom emission type organic light emittingdiode display having the high aperture ratio. Further, using the methodfor manufacturing the thin film transistor substrate having fourelectrodes overlapped each other for forming the three-stack storagecapacitor, it is possible to get a bottom emission type organic lightemitting diode display having the high aperture ratio without increasingof any mask processor number.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is a diagram illustrating the structure of the organic lightemitting diode according to the related art.

FIG. 2 is the exemplary circuit diagram illustrating the structure ofone pixel in the active matrix organic light emitting diode display (orAMOLED) according to the related art.

FIG. 3 is a plane view illustrating the structure of one pixel in theAMOLED according to the related art.

FIG. 4 is a cross sectional view along the cutting line I-I′ forillustrating the structure of the AMOLED according to the related art.

FIG. 5 is a plane view illustrating the structure of a bottom emissiontype organic light emitting diode display according to a preferredembodiment of the present disclosure.

FIG. 6 is a cross sectional view along the cutting line of II-II′ inFIG. 5 for illustrating the structure of an organic light emitting diodedisplay according to the preferred embodiment of the present disclosure.

FIGS. 7A to 7K are cross sectional views illustrating a method formanufacturing a bottom emission type organic light emitting diodedisplay according to the first embodiment of the present disclosure.

FIG. 8 is an enlarged cross sectional view illustrating the structure ofa three-stack storage capacitor electrode in the organic light emittingdiode display according to the preferred embodiment of the presentdisclosure.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Referring to attached figures, we will explain preferred embodiments ofthe present disclosure. Like reference numerals designate like elementsthroughout the detailed description. However, the present disclosure isnot restricted by these embodiments but can be applied to variouschanges or modifications without changing the technical spirit. In thefollowing embodiments, the names of the elements are selected byconsidering the easiness for explanation so that they may be differentfrom actual names.

Hereinafter, referring to FIGS. 5 and 6, we will explain about anorganic light emitting diode display according to a preferred embodimentof the present disclosure. FIG. 5 is a plane view illustrating thestructure of a bottom emission type organic light emitting diode displayaccording to a preferred embodiment of the present disclosure. FIG. 6 isa cross sectional view along the cutting line of II-II′ in FIG. 5 forillustrating the structure of an organic light emitting diode displayaccording to the preferred embodiment of the present disclosure.

Referring to FIGS. 5 and 6, an organic light emitting diode displayaccording to the preferred embodiment of the present disclosurecomprises a switching thin film transistor ST, a driving thin filmtransistor DT connected to the switching thin film transistor ST and anorganic light emitting diode OLED connected to the driving thin filmtransistor DT.

The switching thin film transistor ST is formed where a scan line SL anda data line DL are crossing each other. The switching thin filmtransistor ST selects a pixel for representing video data. The switchingthin film transistor ST includes a gate electrode SG branched from thescan line SL, a semiconductor layer SA, a source electrode SS and adrain electrode SD.

The driving thin film transistor DT drives an organic light emittingdiode OLED of the pixel selected by the switching thin film transistorST. The driving thin film transistor DT includes a gate electrode DGconnected to the drain electrode SD of the switching thin filmtransistor ST, a semiconductor layer DA, a source electrode DS connectedto the driving current line VDD and a drain electrode DD facing with thesource electrode DS and being apart from the source electrode DS with apredetermined distance. The drain electrode DD of the driving thin filmtransistor DT is connected to an anode electrode ANO of the organiclight emitting diode OLED.

Further, the organic light emitting diode display according to thepreferred embodiment of the present disclosure comprises light shieldlayers SLS and DLS disposed under layer of the semiconductor (channel)layer SA and DA formed between the source electrodes SS and DS and thedrain electrodes SD and DD for blocking the external light induced tothe channel layer SA and DA. Especially, each of the light shield layersSLS and DLS is connected to the gate electrodes SG and DG, respectivelyso that the thin film transistors may have the double gate structure.

In addition, under the storage capacitor STG, an additional storagecapacitor electrode TSL may be included. The additional storagecapacitor electrode TSL is formed with the same material and at the samelayer of the light shield layers SLS and DLS. As the additional storagecapacitor electrode TSL is further included, the amount of the storagecapacitor may be increased than the case of without the additionalstorage capacitor electrode TSL.

The amount of the storage capacitor is proportional to the permittivity(or dielectric constant) of the dielectric substance inserted betweenthe two overlapped storage capacitor electrodes, and the surface of thetwo overlapped storage capacitor electrodes. When the additional storagecapacitor electrode TSL is added at the storage capacitor, the amount ofthe storage capacitor may be increased as proportional to the area ofthe additional storage capacitor electrode TSL. In other words, eventhough the surface area of the storage capacitor STG is reduced, due tothe additional storage capacitor electrode TSL, enough amount (or thesame amount) of the storage capacitor can be ensured.

As the present disclosure further includes the additional storagecapacitor electrode TSL, the surface area for forming the storagecapacitor STG can be reduced. As the result, it is possible that theratio of the effective light emission area (i.e., the area of theorganic light emitting diode OLED) to the area of the anode electrodeANO may be increased. That is, the present disclosure suggests a highaperture ration organic light emitting diode display.

Further referring to FIG. 6, we will explain about the cross sectionalstructure of the organic light emitting diode display according to thepresent disclosure. On the substrate SUB, the light shielding layers SLSand DLS are disposed at the area where the semiconductor channel areasSA and DA of the switching thin film transistor ST and the driving thinfilm transistor DT, respectively, will be formed. The light shieldlayers SLS and DLS may be branched from the scan line SL. In that case,the light shield layers SLS and DLS can be used the bottom gateelectrodes, for the case that the switching thin film transistor ST andthe driving thin film transistor DT have the double gate structure.

At the area for the storage capacitor STG, the additional storagecapacitor electrode TLS is formed. The additional storage capacitorelectrode TLS may be formed as an isolated shape having the surface areacorresponding to the storage capacitor. Otherwise, the additionalstorage capacitor electrode TLS may connected to the light shield layerDLS formed under the channel layer DA of the driving thin filmtransistor DT to have one body structure with the light shield layerDLS. Here, in convenience, the drawing for explain the preferredembodiment shows as the additional storage capacitor electrode TLS isextended from the light shield layer DLS of the driving thin filmtransistor DT.

On the whole surface of the substrate SUB having the scan line SL, lightshield layers SLS and DLS and the additional storage capacitor electrodeTLS, a buffer layer BF is deposited. On the buffer layer BF, anintermediate electrode IM overlapped with the additional storagecapacitor electrode TLS is formed.

On the buffer layer BF covering the light shield layers SLS and DLS,semiconductor (channel) layers SA and DA are formed. On thesemiconductor layers SA and DA, the gate insulating layer GI and thegate electrodes SG and DG are formed. The gate electrodes SG and DG areoverlapped with the middle portions of the semiconductor layers SA andDA, respectively. At the both sides of the gate electrodes SG and DG,the source electrodes SS and DS and the drain electrodes SD and DDfacing each other respectively are formed. The drain electrode SD of theswitching thin film transistor ST is connected to the gate electrode DGof the driving thin film transistor DT through a contact hole formed atthe intermediate insulating layer IN. On the whole surface of thesubstrate SUB having the switching thin film transistor ST and thedriving thin film transistor DT, the passivation layer PAS is deposited.

On the passivation layer PAS, the color filter CF occupying the lightemitting area corresponding to the anode electrode ANO is formed. It ispreferable that the color filter CF has as larger area as possible. Forexample, the color filter CF may has the border line as closer to thedata line DL, the driving current line VDD and the scan line SL aspossible. The top surface of the substrate SUB having various elementsincluding the color filter CF is not even but having level differences.In order to make the top surface of the substrate SUB even or smooth, anover coat layer OC may be deposited on the whole surface of thesubstrate SUB.

On the over coat layer OC, the anode electrode ANO of the organic lightemitting diode OLED is formed. The anode electrode ANO is connected tothe drain electrode DD of the driving thin film transistor DT via thecontact hole formed at the over coat layer OC and the passivation layerPAS.

On the substrate SUB having the anode electrode ANO, a bank (pattern) BNcovering the switching thin film transistor ST, the driving thin filmtransistor DT and various lines DL, SL and VDD is formed to define thelight emitting area.

The exposed portions of the anode electrode ANO by the bank BN isdefined as the light emitting area. On the surface of the substrate SUBhaving the bank BN, an organic light emitting layer OLE and the cathodeelectrode CAT are sequentially deposited. Here, the organic lightemitting layer OLE has the organic material radiating the white colorlight. By the color filter CF disposed under the organic light emittinglayer OLE, each pixel can represent colors of the video data. Theorganic light emitting diode display as shown in FIG. 6 is the bottomemission type in which the light for representing the video dataradiates to bottom direction where the substrate SUB is disposed.

Hereinafter, referring to FIGS. 7A to 7K, we will explain about a methodfor manufacturing a bottom emission type organic light emitting diodedisplay according to the preferred embodiment of the present disclosure,in detail. FIGS. 7A to 7K are cross sectional views illustrating amethod for manufacturing a bottom emission type organic light emittingdiode display according to the first embodiment of the presentdisclosure.

As shown in FIG. 7A, on a substrate SUB made of transparent glass orplastic material, an opaque metal material is deposited. By patterningthe opaque metal material using the first mask process, a scan line SL,a light shield layer SLS of the switching thin film transistor ST, alight shield layer DLS of the driving thin film transistor DT and anadditional storage capacitor electrode TLS are formed. The light shieldlayer SLS of the switching thin film transistor ST is formed at an areaoverlapping with the channel area SA of the switching thin filmtransistor ST. The light shield layer DLS of the driving thin filmtransistor DT is formed at an area overlapping with the channel area DAof the driving thin film transistor DT. In some cases, for the dual gatestructure, the light shield layer SLS of the switching thin filmtransistor ST may be branched from the scan line SL. In the interim, theadditional storage capacitor electrode TLS is formed where the storagecapacitor STG is formed. FIG. 7A illustrates that, in convenience, theadditional storage capacitor electrode TLS is extended from the lightshield layer DLS of the driving thin film transistor DT.

As shown in FIG. 7B, a buffer layer BF is formed by depositing aninsulating material on the whole surface of the substrate SUB having thelight shield layers SLS and DLS and the additional storage capacitorelectrode TLS. Depositing a metal material on the buffer layer BF andpatterning the metal material using the second mask process, anintermediate electrode IM is formed. As the result, the first storagecapacitor STG1 is formed at the portions of the buffer layer BF, adielectric material, inserted between the additional storage capacitorelectrode TLS and the intermediate electrode IN.

As shown in FIG. 7C, on the whole surface of the substrate SUB havingthe intermediate electrode IM, a semiconductor material is deposited. Bypatterning the semiconductor material using the third mask process, asemiconductor channel layer SE is formed. The semiconductor channellayer SE includes channel layers SA and DA of the switching thin filmtransistor ST and the driving thin film transistor DT, respectively.Therefore, the semiconductor layer SE has a shape as covering the lightshield layer SLS of the switching thin film transistor ST and the lightshield layer DLS of the driving thin film transistor DT.

As shown in FIG. 7D, on the whole surface of the substrate SUB havingthe semiconductor layer SE, an insulating material and a metal materialare sequentially deposited. By patterning the insulating material andthe metal material at the same time using the fourth mask process, gateelectrodes SG and DG and gate insulating layer GI overlapping with thesemiconductor layer SE and a first storage capacitor electrode SG1.Here, the gate electrode SG of the switching thin film transistor ST isoverlapped with the light shield layer SLS of the switching thin filmtransistor ST. Further, the gate electrode DG of the driving thin filmtransistor DT is overlapped with the light shield layer DLS of thedriving thin film transistor DT. The gate electrodes SG and DG areoverlapped with the some middle portion of the semiconductor layer SEand the both side portions of the semiconductor layer SE are exposed.The middle portions of the semiconductor layer SE is defined as thechannel area SA of the switching thin film transistor ST and the channelarea DA of the driving thin film transistor DT. The exposed sideportions of the semiconductor layer SE are the ohmic areas forcontacting to the source electrode and the drain electrode.

In the interim, the first storage capacitor electrode SG1 is formed asoverlapping with the intermediate electrode IM. As the result, thesecond storage capacitor STG2 is formed at the portions of the gateinsulating layer GI where the first storage capacitor electrode SG 1 andthe intermediate electrode IM. Here, one end portions of theintermediated electrode IM would be exposed. Later, this exposedportions of the intermediate electrode IM may be connected to the secondstorage capacitor electrode SG2 for forming a third storage capacitorSTG3. In another example, some portions of the light shields SLS and DLSmay be exposed by additionally patterning the buffer layer BF. Eventhough in FIG. 7D is not shown, a switching gate contact hole SGHexposing some portions of the light shield layer SLS branching from thescan line SL and a driving gate contact hole DGH exposing some portionsof the light shield layer DLS of the driving thin film transistor DT maybe formed, as shown in FIG. 5. In this case, an additional mask processmay be required. In other method, in the fourth mask process, ahalf-tone mask may be used for saving the additional mask.

As shown in FIG. 7E, on the whole surface of the substrate SUB havingthe gate electrodes SG and DG and the first storage capacitor electrodeSG1, an insulating material is deposited to form an intermediateinsulating layer IN. By patterning the intermediate insulating layer INusing the fifth mask process, the contact holes for exposing the sourceareas and the drain areas of the semiconductor layer SE. Further, acontact hole for exposing some portions of the gate electrode DG of thedriving thin film transistor DT is formed. In addition, a contact holefor exposing the one end portion of the intermediate electrode IM may beformed.

As shown in FIG. 7F, on the intermediate insulating layer IN, asource-drain metal material is deposited. By patterning the source-drainmetal material using the sixth mask process, the source-drain electrodesof each thin film transistor, the data line DL and the driving currentline VDD are formed. For example, a source electrode SS and a drainelectrode DS of the switching thin film transistor ST and a sourceelectrode DS and a drain electrode DD of the driving thin filmtransistor DT are formed. Here, the drain electrode SD of the switchingthin film transistor ST is connected to the gate electrode DG of thedriving thin film transistor DT. In the interim, the drain electrode DDof the driving thin film transistor DT is extended as overlapping withthe first storage capacitor electrode SG1 to form the second storagecapacitor electrode SG2. The second storage capacitor electrode SG2 isconnected to the exposed portion of the intermediate electrode IM. Asthe result, the switching thin film transistor ST and the driving thinfilm transistor DT having the double gate structure are completed.Further, the third storage capacitor STG3 is formed at some portions ofthe intermediate insulating layer IN inserted between the second storagecapacitor electrode SG2 and the first storage capacitor electrode SG1.

As shown in FIG. 7G, a passivation layer PAS is formed by depositing aninsulating layer on the whole surface of the substrate SUB having thethin film transistors St and DT. Depositing a dye material on thepassivation layer PAS and patterning the dye material using the seventhmask process, a color filter CF is formed within the pixel area. When ared color filter, a green color filter and a blue color filter areindividually formed, the seventh mask process may include at least threesub-mask processes. The individual color filter CF is formed within thepixel area surrounded and defined by the scan line SL, the data line DLand the driving current line VDD. In another example, for maximizing thecolor filter CF area, some portions of the color filter CF may beoverlapped with the scan line SL, the data line DL and/or the drivingcurrent line VDD.

As shown in FIG. 7H, on the whole surface of the substrate SUB havingthe color filter CF, an over coat layer OC is deposited. By patterningthe over coat layer OC and the passivation layer PAS using the eighthmask process, a pixel contact hole PH exposing some portions of thedrain electrode DD of the driving thin film transistor DT is formed.

As shown in FIG. 7I, on the whole surface of the substrate SUB havingthe pixel contact hole PH, a transparent conductive material isdeposited. By patterning the transparent conductive material using theninth mask process, an anode electrode ANO is formed. The anodeelectrode ANO is connected to the drain electrode DD of the driving thinfilm transistor DT via the pixel contact hole PH.

As shown in FIG. 7J, on the whole surface of the substrate SUB havingthe anode electrode ANO, an insulating material is deposited. Bypatterning the insulating material using the tenth mask process, thebank BN is formed. The bank BN defines the aperture area, the actuallight emitting area. The bank BN has the shape as exposing most portionsof the anode electrode ANO.

As shown in FIG. 7K, on the whole surface of the substrate SUB havingthe bank BN, an organic light emitting layer OLE and a cathode electrodeCAT are sequentially deposited. As the color filter CF is disposed underthe anode electrode ANO, the organic light emitting layer OLE preferablyhas the organic material radiating the white color light. As the result,the organic light emitting diode OLED including the anode electrode ANO,the organic light emitting layer OLE and the cathode electrode CAT iscompleted. As the anode electrode ANO is connected to the drainelectrode DD of the driving thin film transistor DT, the organic lightemitting diode OLED is driven by the driving thin film transistor DT.

FIG. 8 is an enlarged cross sectional view illustrating the structure ofa three-stack storage capacitor electrode in the organic light emittingdiode display according to the preferred embodiment of the presentdisclosure. Referring to FIG. 8, the organic light emitting diodedisplay according to the present disclosure has the storage capacitorSTG including the first storage capacitor STG1, the second storagecapacitor STG2 and the third storage capacitor STG3. The first storagecapacitor STG1 is formed between the additional storage capacitorelectrode TSL extended from the light shield layer DLS and theintermediate electrode IM. The second storage capacitor STG2 is formedbetween the intermediate electrode IM and the first storage capacitorelectrode SG1. The third storage capacitor STG# is formed between thefirst storage capacitor electrode SG1 and the second storage capacitorelectrode SG2.

Especially, the intermediate electrode IM is electrically and physicallyconnected to the second storage capacitor electrode SG2 and the firststorage capacitor electrode SG1 is inserted between the intermediateelectrode IM and the second storage capacitor electrode SG2. Therefore,the total storage capacitor has the physical and electrical structuresto ensure enough amount of the storage capacitor. The pixel data writtento the drain electrode DD of the driving thin film transistor DT is alsostored to the second storage capacitor electrode SG2 and theintermediate electrode IM. Then, the stored pixel data can be maintainedin the dielectric materials inserted between the additional storagecapacitor electrode TLS and the intermediate electrode IM, between theintermediate electrode IM and the first storage capacitor electrode SG1,and between the first storage capacitor electrode SG1 and the secondstorage capacitor electrode SG2. As the result, when the driving thinfilm transistor DT is off state, the pixel data can be maintained in theanode electrode ANO with the stored electrons in the storage capacitorSTG until next period.

According to the present disclosure, the storage capacitor STG of theorganic light emitting diode display is formed as having three-stackstructure. Therefore, even though the surface area of the storagecapacitor is reduced, the volume of the storage capacitor is notreduced. That is, more electrons can be maintained in the less surfacearea of the storage capacitor. In other words, the area ratio of thestorage capacitor in the pixel area can be reduced. For the bottomemission type, as the area of the storage capacitor can be reducedwithout reducing the amount of the storage capacitor, the light emittingarea can be enlarged. That is, the present disclosure can suggest anorganic light emitting diode display having a high aperture ratio.

While the embodiment of the present invention has been described indetail with reference to the drawings, it will be understood by thoseskilled in the art that the invention can be implemented in otherspecific forms without changing the technical spirit or essentialfeatures of the invention. Therefore, it should be noted that theforgoing embodiments are merely illustrative in all aspects and are notto be construed as limiting the invention. The scope of the invention isdefined by the appended claims rather than the detailed description ofthe invention. All changes or modifications or their equivalents madewithin the meanings and scope of the claims should be construed asfalling within the scope of the invention.

What is claimed is:
 1. An organic light emitting diode display devicecomprising: a plurality of pixel areas disposed in a matrix manner on asubstrate; a thin film transistor disposed in the pixel area; an organiclight emitting diode connected to the thin film transistor and disposedin the pixel area; and a three-stack storage capacitor having fourelectrodes, wherein the three-stack storage capacitor is connected tothe thin film transistor and the organic light emitting diode.
 2. Thedevice according to the claim 1, wherein the thin film transistorincludes: a light shield layer blocking external lights induced to achannel layer and being a lower gate electrode; a buffer layer coveringthe light shield layer; a semiconductor layer having a channel layeroverlapping with the light shield layer on the buffer layer; a uppergate electrode overlapping with the channel layer having a gateinsulating layer there-between; an intermediate insulating layercovering the semiconductor layer and the upper gate electrode; and asource electrode and a drain electrode contact some portions of thesemiconductor layer disposed both sides of the channel layer on theintermediate insulating layer.
 3. The device according to the claim 2,wherein the three-stack storage capacitor includes: a first storagecapacitor formed at some portions of the buffer layer disposed betweenan additional storage capacitor electrode and an intermediate electrodeoverlapped each other; a second storage capacitor formed at someportions of the gate insulating layer disposed between the intermediateelectrode and a first storage capacitor electrode overlapped each other;and a third storage capacitor formed at some portions of theintermediate insulating layer disposed between the first storagecapacitor electrode and a second storage capacitor electrode overlappedeach other.
 4. The device according to the claim 3, wherein theadditional storage capacitor electrode is formed at the same layer andwith the same material of the light shield layer, the first storagecapacitor electrode is formed at the same layer and with the samematerial of the upper gate electrode, and the second storage capacitorelectrode is extended from the drain electrode and connected to theintermediate electrode via a contact hole through the intermediateinsulating layer and the gate insulating layer.
 5. The device accordingto the claim 2, wherein the organic light emitting diode includes: ananode electrode formed on a passivation layer and an over coat layercovering the thin film transistor, and connected to the drain electrodeexposed from the passivation layer and the over coat layer; an organiclight emitting layer deposited on the anode electrode; and a cathodeelectrode deposited on the organic light emitting layer.
 6. The deviceaccording to the claim 5, further comprising: a color filter insertedbetween the passivation layer and the over coat layer and configured todefine a light emitting area.
 7. The device according to the claim 6,wherein the anode electrode includes a transparent conductive material,the cathode electrode includes a reflective metal material, and lightsradiated from the organic light emitting layer radiates to the colorfilter.
 8. A method for manufacturing an organic light emitting diodedisplay, the method comprising: forming a light shield layer and anadditional storage capacitor electrode; forming a buffer layer coveringthe light shield layer and the additional storage capacitor electrode;forming an intermediate electrode overlapping with the additionalstorage capacitor electrode on the buffer layer; forming a semiconductorlayer including a channel layer overlapping with the light shield layeron the buffer layer; forming a upper gate electrode overlapping with thechannel layer and a first storage capacitor electrode overlapping withthe intermediate electrode on a gate insulating layer; forming aintermediate insulating layer covering the upper gate electrode and thefirst storage capacitor electrode and exposing both sides of thesemiconductor layer and one end of the intermediate electrode; andforming a source electrode contacting to one side of the semiconductorlayer, and a second storage capacitor electrode contacting to other sideof the semiconductor layer and the intermediate electrode andoverlapping with the first storage capacitor electrode.
 9. The methodaccording to the claim 8, wherein a first storage capacitor is formed atsome portions of the buffer layer disposed between an additional storagecapacitor electrode and an intermediate electrode overlapped each other;a second storage capacitor is formed at some portions of the gateinsulating layer disposed between the intermediate electrode and a firststorage capacitor electrode overlapped each other; and a third storagecapacitor is formed at some portions of the intermediate insulatinglayer disposed between the first storage capacitor electrode and asecond storage capacitor electrode overlapped each other.
 10. The methodaccording to the claim 8, further comprising: depositing a passivationlayer covering the source electrode, the drain electrode and the secondcapacitor electrode; forming a color filter defining a light emittingarea on the passivation layer; forming an over coat layer covering thecolor filter and exposing some portions of the drain electrode; formingan anode electrode connecting to the drain electrode and covering thecolor filter on the over coat layer; depositing an organic lightemitting layer on the anode electrode; and depositing a cathodeelectrode on the organic light emitting layer.